Traditionally the starting and stopping operations of vacuum cleaners and central vacuum cleaners are carried out by means of switches positioned in connection with the vacuum cleaner, or in the case of a central vacuum-cleaning system, in connection with the suction boxes. In some cases, a conductor is attached to the vacuum cleaner hose so that the switch is within easy reach for the user. In all these cases, the control signals to the central unit of the central vacuum-cleaning system have to be transmitted electrically through fixed electric conductors. With central vacuum cleaning systems, the installation of such conductors causes considerable planning, installation and material costs.
Another problem with prior devices is that the user has to go to the switch in order to start or stop the device. Particularly when in a hurry, e.g. when the telephone is ringing, this is sometimes found inconvenient. Furthermore, the vacuum cleaner hose or the hose of the central vacuum-cleaning system is expensive, heavy and difficult to handle when the conductor is attached thereto. The conductor is also easily damageable in use.
U.S. Pat. No. 4,382,543, in turn, discloses a method for controlling a central unit, in the case of said publication a central heating furnace, with sound or pressure impulses transferred from individual radiators through a return line of a pipe system attached thereto to the vicinity of the heating boiler to be used for the control thereof. Such a method cannot, however, be used for stopping the central unit in connection with a central vacuum cleaning system. This is because of two reasons. Firstly, as sound does not propagate in a vacuum, it is also affected by the variation in the underpressure created by the suction in the vacuum cleaner pipe, and this kind of variation occurs always during vacuum-cleaning. In addition, the vacuum-cleaning air and the rubbish moving within the pipe create varying sounds to such an extent that the use of sound for stopping is unreliable if not impossible.